The synthesis of biologically important bilanes was performed and their interaction with the enzymatic system which gives rise to uroporphyrinogens III and I was examined. The synthesis of the 2-aminomethylbilanes was based on the synthesis of b-bilene hydrobromide, which in turn provide a new approach to porphyrin synthesis. The level of activity of porphobilinogen deaminase was measured in young and mature leaves, and it was found that it disappears previous to senescence. Thus, deaminase is a regulatory enzyme in the biosynthesis of plant porphyrins. Pyrrolooxygenases were measured in different tissues of plants and mammals. A number of synthetic hemines isomeric with the natural hemin IX, were enzymatically oxidized by heme oxygenase to alpha-biliverdins, isomeric with biliverdin IX-alpha. The former biliverdins were reduced by biliverdin reductase to give alpha-bilirubins, isomeric with bilirubin IX-alpha. The enzymatic oxidations, as well as the reduction of the biliverdins, reflect on the mechanism of heme oxygenase, as well as on its substrate specificity.